Naegleria fowleri

What is Naegleria fowleri?

Naegleria fowleri (N. fowleri) is a free-living microscopic amoeba (single-celled organism) commonly found in warm freshwater and soil. There are more than 40 different species of Naegleria but N. fowleri is the only species shown to infect humans. The organism causes a very rare but almost always fatal infection of the brain called Primary Amoebic Meningoencephalitis (PAM).

Where is Naegleria fowleri found?

N. fowleri has been found in many countries throughout the world. Detections have occurred in a variety of warm freshwater environments including dams, waterholes, lakes, rivers, irrigation canals, hot springs, warm water discharge from industrial plants and water supply bores, tanks and pipelines. The organism survives by feeding on bacteria and other microbes in the environment and thrives in water temperatures between 25° and 40°C however growth at temperatures as high as 46°C has been reported.

Inadequately chlorinated long, above-ground pipelines and garden hoses and sprinklers left in the sun can became a breeding ground for N. fowleri. Poorly maintained or undisinfected swimming pools, spas or children’s wading pools can also provide ideal growth conditions for N. fowleri.

In South Australia the organism was historically detected in mains water delivered by lengthy overland pipes (delivering water sourced from the River Murray) where increases in water temperature and a lack of chlorine residual were observed. N. fowleri has not been detected in bore water in South Australia but it has been detected in bore water in other States.While specific testing of rainwater has not been undertaken, no cases of PAM have been linked to rainwater in Australia. Some areas of the River Murray (e.g. where there is low flow, stagnant water and increased water temperatures) could provide favorable growth conditions for the organism. These areas are unlikely to be used for recreational activities. N. fowleri does not tolerate salt water and cannot survive in water that is clean, cool and adequately chlorinated.

How are South Australian water supplies protected?

The introduction of chloramination in the early 1980s to provide longer lasting disinfection virtually eradicated the organism from South Australian drinking water supplies. The likelihood of N. fowleri being present in adequately disinfected mains drinking water supplies is extremely low. SA Water drinking water supplies are extensively monitored to ensure adequate disinfection and protection against pathogenic microorganisms including N. fowleri. Detections in non-drinking water supplies occur occasionally and communities receiving untreated water are provided with written information from SA Water annually regarding practices to reduce the risk of infection with N. fowleri.

How does infection with Naegleria fowleri occur?

PAM occurs when water containing N. fowleri is forced up the nose, usually while swimming, diving or falling into warm freshwater. There have been cases reported where young children have been infected following bathing in untreated water or playing with a garden hose or sprinkler filled with contaminated water. N. fowleri infection has also been reported following the use of untreated water for nasal irrigation (e.g. neti pots). Once in the nose, the organism travels up to the brain where it infects and destroys brain tissue. Disease progression is rapid and recovery from infection is very rare. The median age of infection is approximately 12 years old and infection occurs more predominantly in males, possibly because they are more likely to undertake more vigorous water play.

Infections do not occur as a result of consuming drinking water contaminated with N. fowleri or through use of properly cleaned, maintained and chlorinated swimming pools and spas. Person to person spread does not occur.

How common are Naegleria fowleri infections?

Cases of PAM have been recorded in South Australia, Western Australia, Queensland and New South Wales and in many countries throughout the world.

N. fowleri is frequently found in the environment. It is believed that exposure to this organism is common, but illness is very rare. It has been estimated that the risk from recreational water activities such as swimming, diving and waterskiing in potentially contaminated freshwater in the USA, is five cases of N. fowleri infection for every billion episodes of recreational water activity.

Even if contaminated water does go up the nose, the chance of contracting PAM is extremely low. Why some people become infected with N. fowleri while millions of others exposed to potentially contaminated water do not is unknown.

The last reported case of N. fowleri infection in South Australia occurred in 1981. Recent cases of N. fowleri reported in Australia have been associated with untreated or poorly treated private water supplies.